1. Field of the Invention
This application relates to communication cables. More particularly, this application relates to fiber optic cable design.
2. Description of Related Art
Fiber optic cables, such as loose tube fiber optic cables, are generally constructed with an outer jacket, one or more buffer tubes therein and one or more fibers contained within each buffer tube. The fibers within each buffer tube may also be further contained within a furcation tube. A furcation tube is a small tube that typically contains one UV coated type fiber to protect that fiber for a short distance beyond the coverage of the jacket/buffer tube after stripping.
Generally, when manufacturing loose tube type fiber optic cables, one major concern is fiber length differential, which relates to the difference in length between a buffer tube and the fiber(s) contained therein.
For example, in prior art FIG. 1, an exemplary extrusion line is shown with fibers passing through an extrusion head, with a buffer tube being extruded thereon. In this Figure, the excess length is properly controlled so that the fibers in the buffer tube are substantially straight.
However, as shown in prior art FIG. 2, if the production line is improperly arranged, and the fibers exhibit an excess length relative to the buffer tube, then the fibers will ultimately bunch up within the tube. This results in the fibers having excessive curves within the tube, possibly further exacerbated when the final cable is installed around various curves, resulting in signal attenuation in the fibers.
For example, if the fiber length is too excessive relative to its buffer tube, the fibers may be already bent, or likely to bend on installation, beyond a 15 degree angle resulting in attenuation of signals passing there through due to light escape at the acute bending points. As a separate issue (not shown), if the fibers are too short the tubes and jackets need to be shortened down before the connectors can be added, which is time consuming.
In order to address this, production line products of tubed optical fibers are periodically tested after production to measure excess length to ensure it is within the desired parameters. If it is not, the excess fiber length must be adjusted by altering any one or more than one of the production parameters, such as fiber payoff tension, follow-on tension (set at various drag points), fiber positioning (towards and away from the center of the tube during extrusion), etc. . . . ).
This process of trial and error to get the production line parameters correct, and then maintenance of the production line parameters during continuous use is time consuming.